Electric furnace



Feb, 16 1926. 1,572,894

' G. M. LITTLE ELECTRIC FURNACE Filed Nov. 1, 1922 51 JIII Fig.1.

Fig.5.

WITNESSES; INVENTOR George M. Little Patented Feb. 16, 1926.

UNITED STATES 1,572,894 PATENT OFFICE.

GEORGE M. LITTLE, F PITTSBURGH, PENNSYLVANIA, ASSIGNOR TO WESTINGHOUSE ELECTRIC & MANUFACTURING COMPANY, A CORPORATION OF PENNSYLVANIA.

ELECTRIC FURNACE.

Application filed November 1, 1922. Serial No. 598,817.

To all whom it may concern:

Be it known that I, GEORGE M. LITTLE, a citizen of the United States, and a resident of Pittsburgh, in the county of Allegheny 6 and State of Pennsylvania, have invented a new and useful Improvement in Electric Furnaces, of which the following is a specification.

My invention relates to electric furnaces and particularly to electric-resistance furnaces.

The object of my invention is to provide a relatively simple, rugged and compact furnace structure comprising a'carbonaceous resistor protected against the oxidizing action of surrounding air.

In practicing my invention, I provide a furnace structure comprising a plurality of refractory walls enclosing a furnace cham 29 her in which'is located a heating element comprising a plurality of carbonaceous resistor elements located above a refractory diaphragm dividing the furnace chamber into a work-receiving compartment and a heating" compartment. A double layer of granular refractory material is placed above the resistor to reduce the heat loss therefrom and to prevent oxidation thereof.

In the single sheet of drawings,

Figure 1 is a View, in vertical longitudinal section, of an electric-resistance furnace embodying my invention,

Fig. 2 is a view, in vertical lateral section therethrough, taken on the line II--II of Fig. 1, and

Fig. 3 is avertical sectional view thereof taken on the line III-III of Fig. 1. An electric-resistance furnace, designated generally by the numeral 11, comprises a metallic casing 12 of any suitable or desired contour and dimensions and provided with a plurality of supporting members 13 secured thereto. An outer layer 14, located within the casing 12, comprises a plurality of refractorv bricks or blocks of any suitable heat-insulating material usually employed in the art. 1

An inner layer 15 comprises a plurality of bricks or blocks of a suitable refractory hightemperature-resisting material. The bricks, comprising the two linings, are so located and spacedas to provide a furnace chamber designated generally by the numeral 16 in the drawings. As illustrated more particularly in Figs. 1 and 2 of the drawings, the

furnace chamber may be open at the top, no refractory brick or block roof being provided.

The inner lining 15 is so constructed as to permit of locating therein a refractory plate 17 which dividesthe furnace chamber 16 into two parts, one a work-receiving compartment 18 located below the diaphragm 17 and an upper compartment 19 which constitutes the heating chamber proper. The work-receiving compartment 18 is provided with a suitable opening 20 at one side thereof.

A heating element 21 comprises a plurality of relatively thin, flat, elongated carbonaceous plates 22 which are so located as to have their fiat sides in operative engagement with each other. As illustrated more particularly in Figs. 2 and 3, of the drawings, the plates 22 comprising the heating element 21 may be made of alternately different lengths, although this is not an essential element and is only employed to increase the resistance of the heating element to an electric current traversing the same. The end portions of the plates 22 rest upon suitable shoulders provided by the bricks or blocks of'the' inner lining 15, substantially as illustrated in Fig.- 2 of the drawing. 4

, At each end of the heating element 21 is provided a relatively heavy end block 23 of carbonaceous material, the outer surface of which is operatively engaged by the inner rounded end of an elongated carbonaceous electrode 24. The outer tapering ends of the electrodes 24 are respectively engaged by a water-cooled electric-cirouit-terminal member 25 which is provided with an opening therein adapted to cooperate with and receive the outer tapering end of the electrode.

Compressing means for holding the terminal members 25 in close operative engagement with the electrodes 24 and for compressing the electrodes 24 against the blocks 23 and the plates 22 may comprise a helical spring 26 surrounding a rod 27, the inner end of which is provided with suitable screwthreads to receive a" nut 28 and a washer 29 for operatively engaging the inner end of the helical spring 26. The outer end of the spring 26 engagesa suitable stop member 31, here illustrated as comprising a bent metal strap, the inner end of which is suitably secured against "the metal casing 12. The in ner end of the rod 27 operatively engages the outer surface of an insulating lock 32 which operatively engages the outer surface of the electric-circuit-terminal member 25. By adjusting the position of the nut 28 upon the rod 27, any desired degree of compression may be provided. An insulating ring 30,0f asbestos, may be located at the surface of the furnace structure surrounding the terminal members to preclude leakage of current therefrom. While I have illustrated a specific embodiment of a compressing means, I do not desire to be limited thereto, as any suitable compressing means may be employed. a

The heating element 21 is located above. and closely adjacent to, the upper surface of the diaphragm 17 in order that the length of the path which the heat generated by the heating element, must traverse in order to "reach the heating chamber 18 may beas short as possible.

In order to reduce the loss of heat in an upward direction from the heating element and for simultaneously preventing air from reaching the upper surface of the plates constituting the heating element 21 and oxidizing the same, I provide two layers of granular material. A layer 33 of granular carbon is located immediately above, and in operative engagement with, the upper surface of the heating element 21 and, as i lustrated in Fig. 2 of the drawing, the granular carbon may extend to belovs the upper surface of the. plates at the edges thereof, as far as may be permitted by the shoulder portions of the inner lining upon which the heating elements rest. The inner layer 33 is relatively' thin and an outer thick layer of finely divided material 34, such as coke dust, is provided, the upper surface of which is substantially flush with the upper surface of the two linings of the furnace, substantially as illustrated in Fig. 1 of the drawing.

I have found by actual experiment that the resistance of the built-up heating element 21 is not materially reduced by the superposed layer of coarse granular carbon which, as is well known, is an electric conducting material. The reduction of resistance is so slight as'to be negligible, and the layer of comminuted material, such as coke dust, placed thereabove, effectively reduces the amount of heat which is radiated from the heating element in an upward direction and also reduces to a negligible amount the quantity of air which may filter therethrough and reach the upper surface of the carbonaceous heating element. The oxidizing action upon the heating element from air reaching the same from above is thereby reduced to a ractically negligible amount, whereby the life of the heating element is made of commercial length. I p v The plate 17, comprising a diaphragm between the heating compartment and the open work-receiving compartment, may be made of any suitable or desired material, such as a refractory high-temperature-resisting material usually employed in the art or it may be made of a carbonaceous material, such as carbon or graphite. If it is made of a material other than carbon or graphite, it will not be oxidized by the air entering the workreceiving compartment through the opening 1.9, but, if it is composed of carbon or graphite, it will be attached by the entering air and, in such case, I provide means for counter-acting the oxidizing effect of the en tering air, which may comprise a suitable conduit 35 leading to the material-receiving compartment 18 through the floor thereof, and connected to a suitable source of supply of a hydro-carbonaceous gas. A valve 36 is provided to permit of adjusting the amount of gas permitted to flow into the material-receiving compartment. As the temperature of the diaphragm 17 is relativcly very high. in a furnace of this type, the gas permitted to flow into the materialreceiving compartment 18 is ignited and caused to burn, whereby a sooty vapor is generated and, as this vapor moves in an upward direction, the soot will be deposited against the lower surface of the plate 17, and any oxidizing action of air'entering through the opening 19 is expended on the layer of soot rather than on the plate 17.

The device embodying my invention provides a relatively simple structure c0mprising a minimum number of individual parts effective to prevent oxidization of a carbonaceous resistor of an electric furnace the said means being effective, at the same time, to reduce the heat loss from the heating element,

This application is closely related to my 105 co-pending application, Serial No. 454,776, filed March 23, 1921.

Various modifications and changes in detail and arrangement may be made without departing from the spirit and scope of the no invention, and these are intended to be cov ered by the appended claims.

I claim as my invention:

1. An electric furnace com rising a plurality of refractor walls enc osin a chamher, a refractory p ate dividing sai chamber into a work-receiving compartment and a heating compartment, a heating element in said heating compartment comprising a plurality of elongated, thin, fiat, carbonaceous resistor elements located above said plates, and means comprising comminuted corbonaceous material coverin said heating element for preventing oxidization thereof.

2. An electric furnace com rising a plurality of refractory walls enc osing a chamber, a carbonaceous plate dividing said chamber into a work-receivingcompartment and a superposed heating compartment, a carbonaceous heating'element supported in said heating compartment by said Walls,

means for producing a sooty vapor in said Work-receiving compartment to prevent oxidation of the lower surface of said plate, and a layer of comminuted carbonaceous material on said heating element for preventing oxidation of the upper surface thereof.

In testimony whereof, I have hereunto subscribed my name this 27th day of October, 1922.

GEORGE M. LITTLE. 

